I've read a report about the possible causes of the crash now. It seems that one of the pilots pushed brake during take off by mistake. The brake pedal seem to have "tricky" design (said test pilot Alexander Akimenkov) and you are supposed to put down your foot from it. If not then involuntary break force may be the result during TO.
Mysterious breaking force impeded rotation. PF fought with the stick and pulled too hard so once airborne the AoA of Yak42 exceeded the critical value of 19 deg (optimum range is 10-12), stalled and crashed.
The sole survivor board engineer Sizov who has been traveling as a dead head said that he knew that plane is about to crash. PAX were very nervous during TO because it took too long and when the plane went into air he recognized that crash is inevitable.